Americans tend to be irrational about terrorism. Someone living in the U.S. is thousands of times more likely to die in a car accident than to ever be killed in a terrorist attack. Not only are successful strikes on American soil incredibly rare, but—even in 2001, the year of the 9/11 attack—more people in the U.S. died from falls around the home than from terrorism.

That said, there is one bitter reality every intelligence official I know recognizes: While the probability of a particular American dying in a terror attack is infinitesimal, the chance that the country will be struck by terrorists again is close to 100 percent. Law enforcement and intelligence agencies are extremely skilled at disrupting terror plots, but sometimes the difference between an aborted attack and a successful one amounts to little more than luck.

And from that comes the lesson provided by terrorists that is now almost a mantra for those charged with protecting us. The schooling came on October 13, 1984, the day after the Provisional Irish Republican Army bombed the Grand Hotel in Brighton, England, in hopes of killing Britain’s then-prime minister, Margaret Thatcher. She escaped unharmed, leading the IRA to release a statement that day directed to the British government.

“Today we were unlucky,” the statement read. “But remember we only have to be lucky once. You will have to be lucky always.’’

That’s it: Even if the U.S. thwarts 1,000 terror plots, one will eventually slip by undetected. And national hysteria and excessive politicization of this issue have made it possible for terrorists to accomplish a lot with little effort, meaning the lucky one doesn’t have to be much of a much. Think back to every unsuccessful plot over the past decade, and even the one that worked—the Boston Marathon bombing. Within seconds of detection (or explosion), conservatives raced to the television studios at Fox News to be the first to proclaim that the Obama administration was responsible for what had happened.

Lies and idiocy have been spewed in hopes of spinning tragedy into votes—The Boston bombers should have been sent to Guantanamo! (illegal, since they were American citizens), Obama allowed the real perpetrator to escape! (false, and a claim that led to a slander suit by the man named), George W. Bush never had any terrorist attacks in his time in office! (false—remember 9/11?). Even the recent beheading of journalist James Foley was fodder for attacks on Obama: The president didn’t sound angry enough when he delivered his statement condemning the savagery, and then he played golf!

This fundamentally un-American attempt to politicize something that should unite the country—as happened after 9/11—empowers the terrorists and is more dangerous to the U.S. citizens than the risk of any particular attack. One former intelligence officer told me that, because of this politicization, terrorists now know they can damage an American president—perhaps critically—with even a botched terror attack. Under Bush, a successful strike created a unified, angry giant lashing out at the enemy with all of its might and fury; under Obama, a failed attempt splits the country in partisan—and irrational—bickering. That is the means to the ultimate terror victory.

Which brings us to the latest perceived threat against the homeland, Islamic State (better known as ISIS). In recent days, the heavy breathing out of D.C. has terrified some Americans—ISIS is the biggest danger our country has faced since Al-Qaeda, they have the power to attack our interests, and so on. This time the political war began before an attack against the U.S. was attempted, with conservatives lambasting Obama for not having stopped ISIS in its infancy (which could have been accomplished only by joining forces with President Bashar Assad, the brutal Syrian dictator, in his country’s civil war. And at the time, Republicans threatened to impeach Obama if he went into Syria).

Based on my conversations with intelligence officials and other security experts, saying ISIS is the biggest threat to the homeland since Al-Qaeda circa 2001 is like saying Charles Manson was the biggest threat to the country since Nazi Germany. Sure, both could inflict damage, even ugly, barbaric, horrific damage. But the potential harm is comparable only if—through hysteria and political tribalism—we let it be.

The reason comes down to the different missions, philosophies, goals and capabilities of the two groups. Start with Al-Qaeda just before 9/11. It had a strong, established leadership under Osama bin Laden, including military, operations and financial committees. The group was organized primarily around one major goal—driving the United States out of Saudi Arabia, in part by luring America into a ground war with jihadists. The attacks on the World Trade Center and the Pentagon accomplished that goal, but contrary to bin Laden’s expectations, Al-Qaeda fighters did not rout the Americans. It had years of successful attacks overseas (as well as a number of bungled ones). It maintained significant support throughout the Arab world, something the CIA once measured by the fact that “Osama” became one of the most popular names in the Middle East for baby boys. It maintained bank accounts around the world as part of an extremely sophisticated financial network.

Compare that with ISIS. Its leadership is muddled—the group is led by Abu Bakr al-Baghdadi, but unlike Al-Qaeda, its structure below the top leadership is ad hoc. Its goals are so expansive as to border on the absurd: It hopes to sow civil unrest in Syria and Iraq with the intent of establishing a single, transnational state based on Islamic law. Even in the midst of wars in those two countries, al-Baghdadi has called for ISIS to march on Rome and Spain. As far as the United States goes, its primary interest is to keep America out of a Middle East conflict, which is what the beheading of Foley was all about. And outside of war zones, it has completed no successful terror attacks against the West.

Unlike Al-Qaeda, ISIS is deeply unpopular with large swaths of the Muslim world, including jihadists: It is roundly opposed by the Shiites it attacks ruthlessly, and its brutality with even other Sunnis has undermined support among them. In Syria, jihadist groups combined as the Mujahedeen Army with the goal of driving ISIS out of the country. Al-Baghdadi’s proclaimed merger with Jabhat al-Nusra, an Al-Qaeda affiliate that has legitimacy among Syrians, was annulled by Ayman al-Zawahiri, the successor to bin Laden as head of Al-Qaeda. When ISIS declared a caliphate with al-Baghdadi as the leader, Jabhat al-Nusra secretly approached Zawahiri’s aides to urge him to publicly oppose it.

ISIS has money, but, unlike Al-Qaeda, its financial system is crude and vulnerable. As they do for most jihadist groups, wealthy Sunnis—primarily from Jordan, Syria and Saudi Arabia—pony up cash. Prior to America’s withdrawal from Iraq, Shiites in Iran crossed tribal boundaries to provide ISIS with money in hopes of creating trouble for the U.S. military, but that dried up as soon as the group started slaughtering Shiites. The bulk of its money comes from criminal enterprises such as smuggling and blackmail. According to the Council on Foreign Relations, ISIS obtains as much as $8 million a month by extorting businesses in the Iraqi city of Mosul. But there is no large network of financial groups disguised as charities, nor any of the other advanced techniques used by Al-Qaeda to finance its operations. Given all the battles it is waging, ISIS is more of a hand-to-mouth organization.

Sometimes, even the scariest-sounding successes of ISIS are nothing much. In June, ISIS reportedly seized nuclear material used at the University of Mosul in Iraq and entered the al-Muthanna site located about 60 miles outside of Baghdad, where remnants of former Iraqi leader Saddam Hussein’s chemical weapons program were stored. This might have been cause for concern if Al-Qaeda had done it, given its other capabilities. But, in light of the limited resources of ISIS, the danger that this nuclear material would be used in a dirty bomb, for example, is near zero: Since it is unprocessed, detonating it would be akin to blowing up a box filled with dinner plates. And as for those chemical remnants? Ancient stuff, dating back to before 1991, and probably useless.

ISIS does have one strategic advantage over Al-Qaeda—Twitter. Terrorists have thrived on the social networking system, and ISIS has used it for propaganda and recruiting supporters around the world. And therein lies the real threat to the U.S. The idea that ISIS would launch an attack on the scale of a 9/11—or even something one-tenth as ambitious as that—is far-fetched; it has neither the planning capability, nor the cash, nor the motivation. But what it does have is far too many people living in the West who have been seduced by its polemics online. (Thus the need for the National Security Agency’s terrorist surveillance program, but that’s another thought for another time.) It is those independent groups of two or three supporters living in the U.S. or some other Western country that pose the real danger.

And if that day comes, if ISIS fans in the West get lucky once, America has to react not with cowardice and political gamesmanship but with bravery and unity. During World War II, the British stoically endured almost 37 weeks of strategic bombing in London by the Luftwaffe. They supported their leadership, they went to work and to school, they ate their dinners, they listened to the radio. They didn’t quake in fear.

ISIS can’t hurt the U.S. in any significant way unless Americans let it. Given the group’s limited abilities, dread and American politics are its only means to ultimate success. In other words, Americans have to stop trembling and raging at each other. Doing that will defang ISIS—and any other terrorist group—better than any weapon or surveillance system.